OBJECTIVE: To determine the neural bases of visual deficits that occur during aging and to use the primate visual system for answering general questions about the effects of aging on the brain. RESULTS We have completed an extensive survey of sweep visual-evoked potential (VEP) and pattern electroretinographic (PERG) acuity in all available old (21 to 31 years) rhesus monkeys at the Wisconsin Regional Primate Research Center. The survey included 110 tests from 58 animals (31 young and 27 old). Both cortical (VEP) and retinal (PERG) acuity was significantly lower in the old monkeys. As predicted on the basis of human studies, there was a large overlap in the range of visual acuities at optimal refraction between old and young monkeys. These results demonstrate that the rhesus monkey is an excellent model for the study of central-mediated visual loss during aging. In addition, we have demonstrated that propofol anesthesia does not affect PERG or VEP acuity measurements in young or old animals. We have made progress with our behavioral psychophysics program. We have trained one young adult and one old animal to perform a two-alternative forced-choice visual acuity task. The behavioral and evoked potential survey data will be used to separate groups of animals with good and poor vision for further neurophysiological and anatomical study. FUTURE DIRECTIONS We plan to conduct studies of the sensory properties of single neurons in the primate visual system and relate any functional or morphological changes to age-related deficits in visual abilities previously established with evoked potential and behavioral methods KEY WORDS aging, vision, spatio-temporal acuity